1. Field of the Invention
The present invention relates to a surface laser diode package having a monitor diode for monitoring an optical power of a surface laser diode. The present application is based upon Korean Application No. 96-12985, which is incorporated herein by reference.
2. Description of the Related Art
A general optical disc system, such as a compact disc player, projects laser light on an information recording surface of a disc and reads information recorded on the disc. In this optical disc system, if an output of the laser light varies, an error may occur when a signal is read from the disc. Thus, the optical disc system includes an automatic laser power control (ALPC) servo circuit to stably control the output of the laser light. The ALPC servo circuit includes a photodiode for monitoring an optical power of a laser diode, and controls a driving current of the laser diode according to current flowing through the photodiode. Conventional surface laser diode packages will be described below with reference to FIGS. 1 and 2.
In the surface laser diode package of FIG. 1, a monitor diode 15 has a cylindrical shape wrapping around a surface laser diode 12. The monitor diode 15 detects spontaneous emission beams emitted from the lateral surface of the surface laser diode 12. The detected beams are used to monitor an optical power of the beam emitted from the lateral surface of the surface laser diode 12, and are also used to monitor an optical power of the surface laser diode 12. If a current is applied to an electrode 11 of the surface laser diode 12, the current is supplied to an active region 13, and the surface laser diode 12 generates spontaneous emission beams.
If the current supplied to the active region 13 is greater than or equal to a current value necessary for laser oscillation, the spontaneous emission beams generated from the active region 13 is transformed into a surface laser beam 21 by the laser oscillation. The beam emitted from the active region 13 oscillates between an upper mirror 121 and a lower mirror 123 of the surface laser diode 12, and is emitted outwards via the upper mirror 121 and absorbed into a substrate 14 via the lower mirror 123. The upper mirror 121 and the lower mirror 123, having the active region 13 therebetween, are used as a resonator. Since a current density must be large to generate a surface laser beam 21, a portion of the surface laser diode 12, except a laser oscillation area between the upper mirror 121 and the lower mirror 123, is processed by oxidation or proton implantation to make it a high ohmic layer to thereby enlarge a current density.
The spontaneous emission beams generated by the active region 13 do not completely vanish and is minutely emitted in proportion to the optical power of the surface laser diode 12. The monitor diode 15 receives the spontaneous emission beams emitted from the sides of the surface laser diode 12 when current is applied to an electrode 16 of the monitor diode 15, and outputs a monitor current in proportion to the received beam.
However, the surface laser diode package of FIG. 1 has poor temperature characteristics. If temperature varies, an accurate monitor current cannot be output. Also, spontaneous emission beams 21 are used instead of a surface laser beam to monitor optical power thereby causing an error.
The surface laser diode package of FIG. 2 has a monitor diode 15 installed on a surface laser diode 12. The monitor diode 15 detects part of a surface laser beam 21 emitted from the surface laser diode 12 when current is applied to an electrode 16 of the monitor diode 15. The detected beam is used for monitoring an optical power of the surface laser diode 12.
However, since the monitor diode 15 detects the spontaneous emission beams 21 as well as the surface laser beam emitted from the surface laser diode 12, an error occurs in the optical power monitoring. In addition, since the externally emitted surface laser beam 21 is used, optical power of the surface laser diode 12 is lost and the manufacturing process becomes complicated.